Pharmacological levels of vitamin A compounds and their derivatives have been found effective in reducing the incidence of chemically induced mammary gland tumors. However, the effect of moderately high or marginally low dietary vitamin A on chemically induced mammary tumor incidence has not been examined. The proposed research has two specific aims: 1. To examine the effect of moderately high and marginally low vitamin A supplementation on the initiation of carcinomatous and benign mammary tumors in female rats treated with a single dose of DMBA (Expt. I) and MNU (Expt. II). 2. To examine the effect of moderately high and marginally low vitamin A supplementation on the promotion of carcinomatous and benign mammary tumors in female rats treated with a single dose of DMBA (Expt. III) and MNU (Expt. IV). The many striking parallels between the carcinogen (low-dose)-treated female Sprague-Dawley rat mammary tumor model and human breast tumorigenesis (e.g. hormone responsiveness, frequency of carcinomatous and benign histopathologies, etc.), the capability of examining initiation and promotion separately and the well-known responsiveness of this mammary tumor model to pharmacological doses of retinyl acetate are the major reasons for choosing this experimental animal model in our research proposal. Our long-range goal is to offer a nutritional approach to breast tumor chemoprevention.